For a seatbelt apparatus equipped to protect a vehicle occupant seated in a seat of a vehicle, techniques have been implemented in recent years in which any change in the riding posture of the vehicle occupant is reduced by rapidly restraining the occupant with a belt or webbing in an emergency, when there is instability in the travel state of the vehicle (abnormal operation), or the like.
The restrain control apparatus for a vehicle occupant disclosed in Japanese Patent Application Laid-Open Publication No. 2007-001423 (2007-001423 A) is an example of the prior art related to a seatbelt apparatus for a vehicle. In this apparatus for controlling the restraint on a vehicle occupant, the state of the vehicle requested by the driver of the vehicle is estimated based on a detection result of detection means for detecting the travel state of the vehicle, such as a wheel speed sensor, a longitudinal acceleration sensor, and a lateral acceleration sensor; the sideslip state quantity of the vehicle, which expresses the difference between the estimated state of the vehicle and the current state of the vehicle, is calculated; the frequency of the vehicle sideslip and the average value of the amount of sideslip are computed; and seatbelt adjustment means and operation of the side supports are controlled using the above values so as to increase the restraining force on the vehicle occupant.
In the restraint and control apparatus for a vehicle occupant disclosed in JP 2007-001423 A, the belt adjustment means in the seatbelt apparatus constantly adds up the amount of winding of the seatbelt and performs control in a case in which the frequency of sideslip increases in relation to the travel state of the vehicle, creating a danger that the occupant restrained by the belt will experience discomfort and that the operation of the vehicle will be impeded. In such a seatbelt apparatus for a vehicle, there is a need to adequately restrain the vehicle occupants in accordance with the travel state of the vehicle.